In general, since a tire has a geometry exhibiting symmetry of revolution with respect to an axis of rotation, the geometry of the tire is generally described in a meridian or radial plane containing the axis of rotation of the tire. For a given meridian plane, the radial, axial and circumferential directions respectively denote the directions perpendicular to the axis of rotation of the tire, parallel to the axis of rotation of the tire and perpendicular to the meridian plane.
In what follows, the expressions “radially”, “axially” and “circumferentially” respectively mean “in the radial direction”, “in the axial direction” and “in the circumferential direction” of the tire. The expressions “radially on the inside of and, respectively, radially on the outside of” mean “closer to and, respectively, further away from, the axis of rotation of the tire, in the radial direction, than”. The expressions “axially interior, and, respectively, axially exterior” mean “closer to and, respectively, further away from, the equatorial plane of the tire, in the axial direction, than”, the equatorial plane of the tire being the plane perpendicular to the axis of rotation of the tire passing through the middle of the tread of the tire.
The protective reinforcement of the tire is a cylindrical structure having as its axis of revolution the axis of rotation of the tire. The protective reinforcement extends axially from a first axial end as far as a second axial end over an axial width L and extends radially from a radially interior first face as far as a radially exterior second face over a mean radial thickness T. In the radial direction, the protective reinforcement is a stack of at least one protective layer made up of reinforcing elements or reinforcers that are metal or textile. The reinforcers are coated in an elastomeric compound, namely in a material based on natural or synthetic rubber obtained by blending various constituents. When the protective reinforcement is made up of a stack of at least two protective layers, the axial width L of the protective reinforcement is the axial width of the protective layer of greatest axial width, and the mean radial thickness T of the protective reinforcement is the sum of the mean radial thicknesses of the protective layers. The protective reinforcement is radially on the inside of a tread and radially on the outside of a working reinforcement. The protective reinforcement essentially protects the working reinforcement from attack likely to spread through the tread radially towards the inside of the tire.
The tread is the part of the tire that is intended to come into contact with the ground via a radially exterior tread surface: this is the wearing part of the tire. In the case of an aircraft tire, the tread, comprising at least one elastomeric compound, is usually made up of circumferential ribs separated by circumferential voids known as circumferential grooves.
The working reinforcement, radially on the inside of the protective reinforcement, is also a cylindrical structure having as axis of revolution the axis of rotation of the tire. In the radial direction, the working reinforcement is a stack of at least two working layers usually made up of textile reinforcers coated in an elastomeric compound. In an aircraft tire, the reinforcers of a working layer generally follow, in the circumferential direction of the tire, a periodic zigzag path the amplitude of which defines the axial width of the working layer. The working reinforcement governs the mechanical behaviour of the crown of the tire. The assembly made up of the working reinforcement and the protective reinforcement constitutes the crown reinforcement.
According to current aircraft tire designs, the protective reinforcement is often made up of a single protective layer. The protective layer comprises either metal reinforcements following a wavy path in the circumferential direction of the tire or textile reinforcers having a wavy path in the circumferential direction of the tire or making an angle with the circumferential direction of the tire.
In the case of a protective layer with metal reinforcers following a wavy path in the circumferential direction of the tire, the mass of the protective reinforcement is relatively high given the mass of the metal reinforcers, and this is penalizing in terms of the mass of the tire and therefore of the payload carried by the aircraft.
Whether the protective layer comprises metal reinforcers following a wavy path or textile reinforcers following a wavy path or lying at an angle, it has been found that the protective reinforcement can sometimes be insufficient to prevent the migration of foreign objects from the tread to the working reinforcement, in other words that it may be insufficiently resistant to foreign object damage (FOD). Specifically, given the harsh conditions in which it is used, these being characterized by a high inflation pressure, a high static load and a high speed, an aircraft tire is particularly sensitive to any attack on its tread by a piercing foreign object, which may be present by chance on the runway. In the event of such an attack on the tread, the piercing foreign object, having passed through the protective reinforcement, can progress towards the working reinforcement. If the working reinforcement is completely pierced, this may result in a slow loss of pressure and general damage to the structure of the tire. If the working reinforcement is partially pierced, the retreadability of the tire, namely its ability to have its tread replaced after it has worn away, can no longer be guaranteed.